From the German Patent DE-PS No. 17 56 889, an arrangement is known including a ship's propeller or screw cooperating with a freely pivoted guide wheel trailing the propeller. The guide wheel has a number of blades greater than that of the propeller and a rotational speed which is lower than the one of the propeller. Each blade of the guide wheel has an inner section which is formed as a turbine blade and is disposed within the stream generated by the propeller or screw and another segment which is shaped as a propeller blade and lies outside the screw propeller stream.
In such a driving arrangement, the flow energy contained in the propeller stream behind the ship is partly converted into mechanical energy, of which one part is used for driving the guide wheel and another part is converted by the thus rotated turbine into propulsion energy by those blade segments of the guide wheel which are outside the propeller stream and thus generate a propulsion stream outwardly of the first-mentioned propulsion stream.
For hydrodynamic reasons, such an arrangement allows significant gain of additional propulsion energy in comparison to conventional propellers only when--as I have already mentioned--the number of blades of the guide wheel is greater than that of the main propeller and the rotational speed of the guide wheel or auxiliary drive is lower than that of the main propeller.
Despite the additional investments incurred by such an arrangement in comparison to conventional propellers, the obtained energy recovery is significant, especially when considering the ever increasing fuel costs for ships. On the other hand, such an arrangement has proven to be difficult to design and to construct in view of the complex hydrodynamic relationships involved.